During night, desert plants<span> absorb carbon dioxide and form an intermediate. Then during day time when the stomata is closed to prevent loss of water, they use this stored carbon dioxide to perform </span>photosynthesis<span>.</span>
After 10 years, the isotope would have had two half lives. For each half life, half of the material reacts. Therefore, after one half life, 50% remains. Then, after a second, 25% remains. D is the correct answer.
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